The present invention relates to a power line communications system and, in particular, to such a system that provides through premises power distribution lines highly reliable communication links among signal receiving devices electrically coupled or located in proximity to the premises power distribution lines.
Two main companies that have established many years of success with low cost consumer power line communications equipment are X-10 and Phonex. The X-10 products are the current industry standard for low bandwidth communications over power lines for control applications.
The X-10 technology is incorporated into a wide range of products that meet the low bandwidth requirements, but the X-10 products are far from reliable. In fact, the reliability is sufficiently unreliable that the X-10 technology should not be implemented in life safety devices like smoke detectors and is usually relegated to lighting control applications. The Phonex technology is incorporated into telephone extension and modem extension devices that have higher bandwidth than is needed for control and alarm communication. However, even higher reliability is needed when security or fire alarm messages need to be communicated. What is needed, therefore, is a highly reliable, low bandwidth power line communication technology for the communication of control, alarm, and short messaging data through the power distribution lines in homes and offices.
The present invention is a highly reliable power line communication system that is implemented with a novel power line transceiver. The invention can be incorporated in alarm and control systems, messaging systems, and home server music systems. The addition of an RF bridge and two-way RF communications to power line communications enables use of the power lines as an antenna.
The present invention exhibits the following properties that overcome problems with the existing products that are used for low bandwidth control and alarm reporting applications: much better signal to noise ratios for much higher reliability; signals can couple across line-cuts in emergency alarm conditions; signals couple across phase wiring, so that no phase bridges are required; a significantly higher number of device addresses and message types are available; communication continues even after complete loss of AC power; full two-way communication protocol incorporates error checking; and acknowledgments of all alarm and control messages for high reliability.
These improvements provided by the present invention are accomplished through the six innovations summarized below.
The first innovation entails transmission of signals using the frequency bands between 2-40 MHz, and does not rely on AC zero crossings to communicate. Use of the higher frequency band (2-40 MHz) allows for faster communication baud rates than those used by X-10 products and for significantly more device addresses and message types. Not relying on AC zero crossings, along with the use of battery back-up in life safety and security equipment, allows the equipment to continue communicating even after complete loss of AC power.
The second innovation is the achievement of regulatory approval under Federal Communications Commission (FCC) Part 15 as an xe2x80x9cintentional radiator.xe2x80x9d Power line communication devices have never been listed this way before. However, in the case of life safety equipment, such as smoke detectors or security alarm equipment, it is important to be able to ensure communication even if the power distribution lines become severed or are intentionally cut. Listing a device as an intentional radiator allows for higher transmission power of 10-1000 times more than devices listed as unintentional radiators. This higher power, along with the higher frequencies, also enables signals to easily couple across phases and across severed or broken lines.
The third innovation entails the use of any of the following bands under FCC regulations: 13.553-13.567 MHz, 26.96-27.28 MHz, and 40.66-40.70 MHz for low bandwidth communications requiring extremely high reliability such as for life safety and security alarm and control applications; and 1.705-10 MHz for high bandwidth communications, in which the bandwidth is 10 percent or more of the center frequency, requiring good reliability. These are the only bands in the 2-40 MHz area that the FCC allows for higher power emissions because of the listing as an intentional radiator. (The terms low and high bandwidth are, of course, relative terms. The bandwidth of a band is limited by the difference between the low and high frequencies of the band. The 13.553-13.567 MHz band is, therefore, limited to a bandwidth of 14 kHz, or about 1 percent of the carrier frequencies.)
The fourth innovation entails coupling of communications between the two power distribution lines instead of between one power line and ground. Power line communications devices apparently have not been sold in this configuration before. This reduces a number of problems inherent with grounds and meets the criteria for FCC limits on conducted emissions for intentional radiators.
The fifth innovation entails the addition of an RF signal bridge and two-way RF signal communication to transmit signals from the power distribution lines, using them as an antenna.
The sixth innovation entails the use of an RF signal bridge to implement two-way communication between battery operated devices.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying drawings.